The present invention relates to an automatic automotive headlamp leveling device and more particularly to an automatic automotive headlamp leveling device for automatically adjusting the optical axes of the headlamps based on a pitch angle of the vehicle detected generally while the vehicle is not moving.
In constructing a headlamp, a reflector in which a light source is securely inserted can be supported tiltably about a horizontal tilting axis relative to a lamp body. The optical axis of the reflector (headlamp) can be tilted about the horizontal tilting axis.
While the vehicle is stationary, a pitch angle of the vehicle may change relative to a reference position when a load is placed in or unloaded from the vehicle or when passengers get in or out of the vehicle. However, in most cases the vehicle lowers both at the front and rear. Because of this, a single vehicle height sensor of a one-sensor system is provided, for example, on a rear suspension to correlate the vehicle height (a vertical distance between a rear axle and the vehicle body) at the rear with the pitch angle of the vehicle. Thus, an approximate straight line, which comprises control data that correlate an output from the vehicle height sensor with the pitch angle of the vehicle, is obtained. The assumption associated with the line is that the front of the vehicle is also lowered. A pitch angle is then calculated based on an output from the vehicle height and the approximate straight line (control data).
As shown in FIG. 9, a conventional automatic automotive headlamp leveling device comprises the following: an actuator 102 for vertically tilting an optical axis L of a headlamp 100 relative to the vehicle body for adjustment, a vehicle height sensor 104 provided on a suspension on either the left or right rear wheel for detecting a distance between an axle and the vehicle body, and a control unit 106. Data from the vehicle height sensor 104 and pitch angles data of the vehicle reside in the control unit 106 as correlation functions (control data that are represented approximately as straight lines). The control data therein are used to calculate a pitch angle of the vehicle based on an output from the vehicle height sensor 104. The actuator 102 is controlled by an amount corresponding to the calculated pitch angle.
When A static load that acts on the vehicle is changed, the vehicle height sensor 104 detects and sends the change to the control unit 106. The control unit 106 calculates a vehicle pitch angle based on the correlation function that correlates vehicle height sensor outputs with vehicle pitch angles that are already entered and set in the unit 106. The unit 106 also drives the actuator 102 (tilts the optical axis about the horizontal tilting axis) by an amount corresponding to the calculated vehicle pitch angle and adjusts the optical axis L of the headlamp 100 such that the optical axis stays in a predetermined inclined or tilted angle relative to the road surface at all times.
In a two sensor system, a vehicle height sensor is provided on the front and rear suspensions, respectively. The control unit 106 calculates a vehicle pitch angle from "THgr"=tanxe2x88x921(h/D), where "THgr" is the vehicle pitch angle, h (=H1xe2x88x92H2) is the difference between the output H1 from the front vehicle height sensor and the output H2 from the rear vehicle height sensor, and D is the distance corresponding to the wheel base of the vehicle.
With the conventional automatic headlamps leveling device described above, the vehicle pitch angle is set to 0 when only the driver is in the vehicle. Also the optical axis L is inclined to a predetermined angle relative to the road surface when the actuator 102 (a longitudinal driving member thereof) is positioned at a front-most end position P1. Since the vehicle pitch angle (the optical axis of the headlamp) changes upwardly only when the static load of the vehicle increases because of, for example, additional passengers, the optical axis of the headlamp only has to be tilted downwardly for adjustment. Therefore, the actuator (the longitudinal driving member thereof) is constructed to move only rearwardly where the front-most end position P1 is set as the initial position. The driving of the actuator is controlled on the assumption that the front-most end position P1 of the longitudinal stroke of the actuator coincides with the initial position P0 at which the vehicle pitch angle is 0. Note that reference numeral P2 denotes a rear-most end position of the longitudinal stroke of the actuator.
However, the front-most end position of the actuator may not necessarily match the initial position PO because of vehicle assembling error, mounting error of the vehicle height sensor on the suspension, or output voltage-related error of the vehicle height sensor itself (hereinafter, these errors are referred to in general as the mounting errors of a vehicle height sensor or the like). If the optical axis L is adjusted to a proper position L0 by tilting the reflector using the aiming mechanism 108, the assembling error of the mounting errors of the vehicle height sensor or the like can be corrected. However, offer errors such as errors associated with the mounting of vehicle height sensor to the suspension or the output voltage-related error of the vehicle height sensor itself (hereinafter, referred to as the mounting tolerance of the vehicle height sensor itself) remain uncorrected.
FIG. 10 shows a case where the signal voltage of the vehicle height sensor is offset in a direction in which the optical axis is raised (V1xe2x86x92V0) because of the mounting tolerance of the vehicle height sensor. The same figure shows the optical axis position at which the vehicle pitch angle is zero (0) when only the driver is in the vehicle. This position corresponds to a position P0, which is further ahead of the front-most end position P1 of the longitudinal stroke of the actuator. Even if the optical axis is adjusted to the proper position L0 using the aiming mechanism 108, the positional relationship between the front-most end position P1 of the longitudinal stroke of the actuator and the initial position P0 of the vehicle pitch angle "THgr" remains unchanged. The issue of the mounting tolerance of the vehicle height sensor itself still exists. Therefore, between signal voltages V0 and V1 of the vehicle height sensor, the optical axis always constitutes a dead zone corresponding to the front-most position P1 of the actuator, preventing the proper leveling of the headlamp.
The actuator is constructed such that it operates only in the direction in which the optical axis is lowered. However, since the front-most end position P1 of the longitudinal stroke of the actuator is not properly set (the front-most end position P1 of the longitudinal stroke of the actuator does not coincide with the initial position P0) when the rear of the vehicle is lowered, a dead zone is produced while signal voltages V0 to V1 of the vehicle height sensor are outputted. Thus, the pulling-in operation of the actuator is interrupted. Because of this, an operation of lowering the optical axis is started after the optical axis is tilted upward by an angle xcex94"THgr"xe2x80x2 corresponding to the mounting tolerance of the vehicle height sensor, which is an angle corresponding to the signal voltages V0 to V1 of the vehicle height sensor. Hence, the driver of a on-coming vehicle may suffer from glaring lights.
The present invention was made in view of the problem described above. An object of the present invention is to provide an automatic automotive headlamp leveling device for enabling a highly accurate optical axis correction by controlling the driving of an actuator without being affected by the mounting tolerance of the vehicle height sensor.
To attain the above object, according to a first embodiment of the invention, there is provided an automatic automotive headlamp leveling device comprising headlamps optical axes adapted to tilt vertically relative to a body of a vehicle by driving actuators, a vehicle height sensor provided on a suspension of the vehicle for detecting a vertical distance between an axle and the body, and an arithmetic control unit for calculating a vehicle pitch angle corresponding to an output from the vehicle height sensor based on a predetermined expression and for controlling the driving of the actuators based on the calculated pitch angle. The actuators are each constructed to operate only in a direction in which the optical axes are lowered from a front-most end position or rear-most end position of a longitudinal stroke of the actuators in which the vehicle pitch angle is zero (0) with the optical axes being in a predetermined inclined state relative to a road surface.
The control unit is operated on the assumption that initial positions of the actuators are positions that are offset from the front-most end positions or rear-most end positions of the longitudinal strokes of the actuators by at least an amount of stroke corresponding to a maximum mounting tolerance in a direction in which the optical axes are lowered. The control unit further subtracts an output corresponding to the offset value from an output from the vehicle height sensor, calculates a vehicle pitch angle corresponding to the offset subtracted output based on the predetermined expression, and controls the driving of the actuators relative to the assumed initial positions based on the pitch angle calculated as corresponding to the offset subtracted output.
The control unit can comprise an ECU, which is an integration of a CPU, a RAM and a ROM. In a one-sensor system in which a vehicle height sensor is provided on a rear suspension, the vehicle pitch angle "THgr" and the output H from the vehicle height sensor can be approximated by a control line, which is a first-order line expressed as "THgr"="THgr"oxe2x88x92kH, where "THgr"o is a maximum pitch angle of the vehicle body, and k is a constant. The relational expression (a control line) is entered and set as an expression in the control unit.
Additionally, in a two-sensor system in which vehicle height sensors are provided on both the front suspension and the rear suspension, respectively, the vehicle pitch angle "THgr" is expressed as tan "THgr"=h/D, where an output from the front vehicle height sensor is H1, an output from the rear vehicle height sensor is H2, a difference between the outputs from the two sensors is h (=h1xe2x88x92H2), and the wheel base is D. This relational expression is entered and set as an expression in the control unit.
In addition, the maximum mounting tolerance of the vehicle sensor can be obtained from experience, and an offset amount of the initial position of the actuator (the assumed initial position of the actuator) and an output from the vehicle height sensor corresponding to the offset amount can be determined.
The control unit is constructed to assume an initial position of the longitudinal stroke of the actuator a position that is offset from the front-most end position or rear-most end position of the longitudinal stroke of the actuator in a direction in which the optical axis is lowered by at least an amount of stroke corresponding to the maximum mounting tolerance of the vehicle height sensor. Additionally, the arithmetic control unit subtracts an output corresponding to the offset value from an output from the vehicle height sensor, calculates a vehicle pitch angle corresponding to an offset subtracted output based on a predetermined expression and controls the driving of the actuator relative to the assumed initial position based on the pitch angle corresponding to the offset subtracted output.
When the vehicle pitch angle changes because, for example, a passenger steps into the vehicle (vehicle body), the vehicle sensor detects this change. Then, the control unit calculates a vehicle pitch angle corresponding to an output from the vehicle height sensor based on the predetermined expression and controls the driving of the actuator such that the pitch angle is cancelled or that the axis of the headlamp is maintained at a predetermined angle relative to the road surface at all times.
In particular, the control unit is configured to assume a position offset from the front-most end position or rear-most end position of the longitudinal stroke of the actuator by at least an amount of the stroke corresponding to the maximum mounting tolerance of the vehicle height sensor in the direction in which the optical axis is lowered as the initial position of the longitudinal stroke of the actuator. The control unit obtains a vehicle height sensor output from which the mounting tolerance of the vehicle height sensor is removed (Hxe2x88x92xcex94H) (which excludes the mounting tolerance) by subtracting a vehicle height sensor output (xcex94H) corresponding to the offset amount of the actuator initial position from an output (H) detected by the vehicle height sensor. Following this, the arithmetic control unit calculates a vehicle pitch angle corresponding to the vehicle height sensor output from which the mounting tolerance is removed (Hxe2x88x92xcex94H) by using an expression "THgr"="THgr"oxe2x88x92kH for the one-sensor system or by using an expression "THgr"=tanxe2x88x921(h/D) for the two-sensor system, respectively. That is, the control unit calculates the vehicle pitch angle based on a control line (broken B) expressed as "THgr"="THgr"oxe2x88x92k(Hxe2x88x92xcex94H) instead of a control line shown in FIG. 3 expressed as "THgr"="THgr"oxe2x88x92kh (solid line A) for the one-sensor system or calculates the pitch angle based on an expression "THgr"=tanxe2x88x921((hxe2x88x92xcex94h)/D) for the two-sensor system. Then, the control unit controls the actuator such that the actuator tilts the optical axis relative to the initial position by an amount corresponding to the pitch angle from which the mounting tolerance is removed.
For example, assume that the initial position of the actuator is located at a position offset from the front-most end position P1 of the longitudinal stroke of the actuator shown in FIG. 10 by an amount of the stroke corresponding to the maximum mounting tolerance of the vehicle sensor in the direction in which the optical axis is lowered, and also assume that this initial position is shown by reference numeral P0xe2x80x2 in FIG. 10. Furthermore, assume that an output from the vehicle height sensor then is V0xe2x80x2. If the signal voltage of the vehicle height sensor is offset by xcex94V(=V1xe2x88x92V0) in a direction in which the optical axis is raised because of the mounting tolerance, an output voltage can be offset by xcex94Vxe2x80x2(=V0xe2x80x2xe2x88x92V1) in an opposite direction to the offset direction of the signal voltage because of the mounting tolerance, i.e., in the direction in which the optical axis is lowered. Then, since xcex94Vxe2x80x2 greater than xcex94V, the output from the vehicle height is transmitted in terms of a position behind the front-most end position P1 of the actuator. Even if the vehicle height sensor signal voltages are between V0 and V1, which fall on the dead zone, the actuator can operate to withdraw without any delay because the output can be detected between V1 and V0xe2x80x2, thereby eliminating the risk of generating any glare.
According to a second embodiment of the invention, there is provided an automatic automotive headlamp leveling device comprising headlamps optical axes adapted to tilt vertically relative to a body of a vehicle by driving actuators, a vehicle height sensor provided on a suspension of the vehicle for detecting a vertical distance between an axle and the body, and an control unit for calculating a vehicle pitch angle corresponding to an output from the vehicle height sensor based on a predetermined expression and controlling the driving of the actuators based on the calculated pitch angle. The actuators are each constructed to operate only in a direction in which the optical axes are lowered from a front-most end position or rear-most end position of a longitudinal stroke of the actuators in which the vehicle pitch angle is zero with the optical axes being in a predetermined inclined state relative to a road surface. The control unit is operated on the assumption that positions that are offset from the front-most end positions or rear-most end positions of the longitudinal strokes of the actuators by at least an amount of stroke corresponding to a maximum mounting tolerance in a direction in which the optical axes are lowered as initial positions of the actuators. The control unit further adds a pitch angle corresponding to the offset value to the vehicle pitch angle calculated based on the predetermined expression and controls the driving of the actuators relative to the assumed initial positions based on the offset value added pitch angle.
According to the second embodiment of the invention, the control unit is constructed to assume as the initial positions of the actuators the positions that are offset by at least an amount of the stroke corresponding to the maximum mounting tolerance of the vehicle height sensor from the front-most end positions or rear-most end positions of the longitudinal strokes of the actuator.
The control unit calculates the vehicle pitch angle corresponding to an output H from the vehicle height sensor including the mounting tolerance of the vehicle height sensor from the expression "THgr"="THgr"oxe2x88x92kH for the one-sensor system and from the expression "THgr"=tanxe2x88x921(h/D) for the two-sensor system. Obtained from the result of the operation (the pitch angle including the mounting tolerance) is a vehicle pitch angle from which the mounting tolerance is removed (not including the mounting tolerance) ("THgr"+xcex94"THgr") by adding a vehicle pitch angle xcex94"THgr" corresponding to the offset amount of the actuator initial position (FIG. 3). To tilt the optical axis by an amount corresponding to the vehicle pitch angle from which the mounting tolerance is removed ("THgr"+xcex94"THgr"), the driving of the actuator is controlled relative to the assumed initial position.
In addition, according to a third embodiment of the invention, an automatic automotive headlamp leveling device as set forth in the first or second embodiment of the invention is provided such that the optical axes of the headlamps are constructed to be tilted for adjustment with an aiming mechanism, and the offset amount of the assumed initial position is set to be equal to an amount of the stroke corresponding to a maximum mounting tolerance.
If the optical axes of the headlamps deviate from proper positions at the front-most end position or rear-most end position of the longitudinal stroke of the actuator, the optical axes can be tilted for adjustment to the proper positions with the aiming mechanism.
Additionally, since the offset amount of the assumed initial position of the actuator is limited to the amount of stroke 6 corresponding to the maximum mounting tolerance of the vehicle height (FIG. 2), as shown in FIG. 10, an area corresponding to the automatic headlamps leveling in the longitudinal stroke P1 to P2 of the actuator is an area P0xe2x80x2 to P2. Thus, the reduction in area corresponding to the automatic headlamps leveling is kept limited (the stroke amount corresponding to the maximum mounting tolerance of the vehicle height sensor), and therefore, the reduction in automatic headlamps leveling range can be suppressed to that extent.
According to a fourth embodiment of the invention, an automatic automotive headlamp leveling device as set forth in any of the embodiments 1 to 3 is provided such that the automatic leveling device comprises vehicle speed detecting means, acceleration detecting means and stable running time detecting means. The control unit controls the driving of the actuators while the vehicle is stationary or while the vehicle is running stably where the speed of the vehicle is equal to or faster than a predetermined value and the acceleration thereof is equal to or lower than a predetermined value for a predetermined period of time continuously. The control unit also calculates a vehicle pitch angle corresponding to an output from the vehicle height sensor detected during the stable running to control the driving of the actuators based on the calculated vehicle pitch angle.
The automatic headlamps leveling sometime may have to be carried out under an unsuitable condition such as when a vehicle is parked partially on a curb. However, an improper leveling of this type can be corrected because the vehicle pitch angle can be calculated easily when the vehicle is running stably to produce constant vehicle height sensor outputs. The vehicle pitch angle is calculated from the vehicle height sensor output, and the driving of the actuator is controlled based on the vehicle pitch angle.